Petroleum as it is naturally produced from an underground formation, is in most cases a mechanical mixture of oil, entrained gas and salt water, some of which latter may be present as an oil/brine emulsion. It is desirable, and usually necessary to treat the petroleum thus produced at the wellhead, for the separation and removal of the entrained gas and emulsified brine, in order to render the oil pipelineable. Usually, the separated salt water is pumped back into the formation, in order to assist in maintaining the pressure therein, and also to resolve the salt water disposal problem. Separated gas is vented or flared, if in small quantities, and if in commercial volumes, is delivered to a pipeline for distribution. The equipment used for this three-phase separation is known as a treater, and is generally quite familiar to those to whom the present invention will be addressed.
Such treaters normally involve the heating of the produced petroleum, in order to lower the viscosity of the fluid phase, and also to assist in the separation of the entrained gas. Brine droplets are coalesced either mechanically, as by forcing the emulsion through a series of perforated baffles; or electrostatically as by forcing the emulsion through a high-energy, electrically charged field; or chemically, by means of surface-active chemical agents which reduce the surface tension on the water droplets, thereby allowing them to coalesce into larger drops for separation by gravity. Frequently, two or more coalescing methods are employed in a treater.
Treaters have evolved in design from early developed open vats which maintained the produced petroleum in stationary condition for several days, permitting the entrained gas to freely separate to atmosphere and the salt water to separate to the bottom of the vat by gravity. There evolved heating methods in order to expedite the treatment by reducing the viscosity of the oil, as described. Subsequent development evolved the heater-treater which is the current state-of-the art comprising an elongated enclosed tank having a burner-fired heater section and a downstream treater section for a continuous flow, with a series of perforated baffles positioned within the treater section transversely to the flow of fluids; the perforated baffles function to promote the even distribution over the full cross-sectional area of the treater section of the fluids in motion, and to cause a pressure drop within the fluid across the perforated baffles which results in a release of entrained gases, which then collect in the upper volume of the tank for removal. However, salt water emulsions within the oil have continued to be inefficiently treated by gravity settling and baffling of the flow following heating: thus, further measures have been necessary in order to cause coalescing of the small droplets of brine into larger drops which could be settled out by gravity.
The conventional treatment has the operational disadvantages of being time-consuming, due to the residence-time required in the treater and the requirement that the petroleum be heated to a sufficiently high temperature to reduce the viscosity thereof so that coalescing of the emulsified droplets will be encouraged. The maintenance of a large quantity of oil at a relatively high temperature is costly of energy, and requires the equipment involved to be capable of sustained operation at the temperatures involved.
Treaters in current use are normally tanks in the form of elongated horizontal cylinders divided by means of internal partitions into compartments through which the petroleum will sequentially flow. Burner-fired heaters are normally included in the upstream heater section for heating the emulsion to the desired temperature, during which most of the entrained gas and some of the brine will separate from the emulsion. The partially demulsified brine then flows into a treater section, in substantially gas-free state, encountering a series of baffles adapted to encourage even flow of fluids and to avoid the formation of flow channels within the fluid body, thereby to assist in separation of remaining gases and coalescing of water droplets, and their separation by gravity to the bottom of the tank for ultimate discharge removal.
Various techniques of improvement have heretofore been employed in order to minimize treatment time and heat energy consumption. In my U.S. Pat. No. 4,329,159, "Energy Saving Heavy Crude Oil Emulsion Treating Method and Apparatus for Use Therewith" (which is incorporated herein in its entirety by this reference), there is described a method and apparatus of the type described, additionally including a number of metallic apertured grid electrodes suspended adjacent apertured baffles, the electrodes being supplied with electrical energy. A series of longitudinally spaced electrical fields of high potential are thereby created, which cause droplets of emulsified brine to move in violent random fashion, the droplets coalescing and collecting into drops of sufficient weight as to fall by gravity to the lower portion of the treater section for removal.
In my U.S. Pat. No. 4,919,777, "Electrostatic/Mechanical Emulsion Treating Method and Apparatus" (which is incorporated herein in its entirety by this reference), there is described an improved method and apparatus of this type, wherein, immediately downstream of the apertured grid electrodes, the flow is directed downwardly through a plurality of inclined open-ended tubes arranged in bundle-fashion.
Unfortunately, most such prior art methods and the apparatuses are inherently inflexible in operation. The apparatuses are designed for a narrow range of operating parameters, such as flow rate, oil/water ratio, salinity, temperature, viscosity, etc. After the apparatuses are manufactured and installed, they are only effective when operating within these narrow design operating ranges. When operating conditions change, an entirely new apparatus must be designed, built and installed. This is a special problem for crude oil producers, because crude oil/water emulsions produced in an oil field can vary dramatically from well to well, and even within the same well from day to day.
Accordingly, there is a need for further improvements in methodology and apparatuses which will overcome these problems in the prior art.